115 - Functional Morphology of the Sea Lamprey (Petromyzon Marinus) Integument

Poster Board Number: 115
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Abstract Body : Sea Lampreys are capable of a wide range of movements from undulatory swimming to twists and torsions when building nests and spawning. When the trunk is bent and twisted, the skin must deform accordingly without drag-inducing wrinkles. The skin also has a role as part of the body’s hydrostatic skeleton since the lampreys lack hard skeletal structures in their trunk. The underlying morphology responsible for these roles was investigated with microdissection and histology. The skin (i.e., the epidermis and dermis) is anchored to the central notochord by connective tissue fibers that traverse the hypodermis. The epidermis is covered by a cuticle and rests on the basement membrane. It comprises three types of cells: Mucous, granular and skein cells. Mucous cells are the smallest and most numerous cell type and are stacked six to eight cells deep. In relaxed skin areas (e.g., on the inner side of a bend), the mucous cells are elongated radially atop a wrinkled basement membrane, whereas in stretched areas (e.g., on the outer side of a bend), they are cuboidal atop a smooth basement membrane. This variation suggests that the epidermis may function like a transitional epithelium. Granular cells occupy the upper epidermal layers underneath the cuticle with a granular cytoplasm and a central nucleus. The solitary skein (sic!) cells are the largest epidermal cells and are interspersed amongst the mucous cells. They extend from the basement membrane to the epidermal surface and contain helically coiled filaments. The dermis underneath the basement membrane comprises two distinct layers: The superficial layer with relatively thin fiber bundles that arise obliquely from the basement membrane and interweave loosely near their origin before forming 5-7 layers of left- and right-handed helically arranged fiber bundles into a cross-fibered helical array; and the deep layer with tightly packed thicker collagen fiber bundles that form a helical array of 20-25 layers of fibers with an angle of ca. 50 degrees to the long axis. Radially oriented fiber bundles also arise from the basement membrane and pass through the helical array toward the hypodermis. As they traverse the dermis, they exchange smaller fiber bundles with the layers of the helical array. Radial and helical fibers leave the deep layer of the dermis to join the connective tissue myosepta and the perimysial fiber bundles, which surround the muscle fibers of the myomeres, to continue through the trunk musculature to anchor onto the notochord. Contraction and shortening of the longitudinally oriented trunk muscle fibers lying between the hypodermis and notochord result in a radial expansion, which is resisted by the radial and helical fibers in the dermis and, thereby, causes a rise in the internal pressure of the trunk. As a result, the skin of lampreys functions as the inextensible envelope of a classic hydrostatic skeleton by ensuring a constant volume, while the cross-fibered helical array enables the bending of the trunk without kinking. Funding was provided by a Sigma Xi Grant in Aid of Research to BMW and the LSU Foundation to DGH.